1. Field of the Invention
This invention relates to voltage regulation in a DC power supply. In particular, a high bandwidth, low dropout linear regulator for use in highly dynamic load environments is disclosed.
2. Background of the Invention
State of the art circuits, such as CMOS VLSI technology have proven to be extremely dynamic loads. It is not unusual for such circuits to exceed steady state operating current by over 100% during switching. Placing these circuits in centralized power systems is not feasible because the voltage at these integrated circuits will drop beyond their specified operating range due to inductive losses in the power distribution.
Conventional solutions include putting a linear regulator on a circuit card. This solution, however, requires a 2.5 volt drop across the regulator, resulting in power dissipation in excess of than 12.5 watts for a 2.5 volt drop. Low dropout regulators reduce the voltage loss to about 1 volt and power dissipation of 5 watts.
This solution, however, is not satisfactory because commercially available linear regulators have a low bandwidth. As a result, the dynamic response of the power supply is inadequate. A typical regulator, such as a Model 7805 (5 volts, 1 amp) has a 600 mV drop for a 500 mA step load, and its output impedance is greater than 1 ohm above 50 KHz.
It is desirable to have a linear regulator with the following characteristics:
1) wide bandwidth to decrease the amount of external filtering required to meet dynamic load requirements and improve load rejections; PA1 3) scalable with respect to current and parallelable for large loads; and PA1 4) capable of being integrated into an application specific integrated circuit (ASIC) for power applications.